The behavior of clayed materials is of central interest in the design of high-level radioactive waste (HLW) repositories because of their potential involvement as:

• raw material to construct the man-made engineered barrier envisaged around the waste canister;
• backfill-clay mixture planned to stabilize the disposal galleries and prevent water entering through the tunnel;
• raw material to manufacture seals for mined and very deep borehole isolation concepts; and
• geological barrier in mined repositories in claystone formations.

In recent years significant advances have been made on the Thermo-Hydro-Chemo-Mechanical (THCM) behavior of engineered barriers and surrounding rocks. However there are yet important features associated with this problem that need further research; such as the understanding and modeling of preferential pathways for the flow of fluids in EBS. The presence of preferential paths is inherent to the design of HLW repositories and they can appear in different forms in the EBS.

The main goal of this project is to gain a better understanding on the possible effects of gas migration (particularly through discontinuities) on the performance and long term behavior of engineered barrier systems (EBS) envisaged for the isolation of HLW. Fundamental, experimental, and numerical investigations are being conducted to accomplish this objective.

• The fundamental studies are aimed at gaining a better understanding of the phenomena controlling gas migration in EBS.
• The experimental activities are focused on replicating in the lab under controlled conditions plausible scenarios that may lead to the development of preferential pathways in EBS. Flow of fluids and transport properties through discontinuities are investigated in the laboratory under controlled THM conditions.
• The numerical investigation is advocated to extend a current modeling framework to deal with pre-existing (e.g. interfaces) and evolving (e.g. cracks) discontinuities in EBS materials. .

The final aim is to improve the current understanding of degradation processes in engineered barrier materials (e.g. drying induced cracks and clay structure changes), and also, to contribute to advance current knowledge on water and gas transport processes through engineered and natural materials, particularly through discontinuities. A better understanding of gas flow processes through geological and engineered barriers will assist to a better prediction of the long-term performance of repositories for HLW waste, leading to a better design of this type of isolation system preventing the release of pollutants to the geosphere

This project is based on a research collaboration between Texas A&M University (TAMU) and international collaborators from Spain.